Problem: AGOL uses a proxy (proxy.ashx) of its own, which is not configurable. This creates a protential problem to use AGOL out of box to access data sources where the proxy can't access.
We plan to use AGOL as our primary collaboration site for our geospatial professionals. One of the requirements is that internal users must be able to create and configure maps that use internal data sources. Since those data sources are hosted behind firewalls and not accessible from internet, any proxy.ashx hosted at AGOL will not work with those maps.
Proposed Solution: 1. Make a configuration for a default proxy.ashx Url for the whole AGOL organizational site. 2. Make the proxy Url configurable for each map. 3. Make the proxy Url configurable for each layer in a map.